Design and development will be constrained if you don’t have content to design and build with. Content is hard, but content is ultimately more important than both the design and development. It’s what people see and interact with. Good design and development should be ‘invisible’. Start with content first. Yes, it will change as you go along but it will give you and the team a framework to work around. It allows you to test with real data. It lets you see if things are working or not. It makes things feel real.